We hear disputes about what exactly the Black Plague was, or what the English Sweat was, as if all the mystery diseases are far in the past. But there are some diseases that have flared up and died down in the last century, without anyone knowing exactly what caused them.

Lytico Bodig was almost unknown before World War II. A few residents of Guam, primarily the Chamorran people in southern Guam, died in 1904 from a disease that resembled it. It seemed like a slow-progressing paralysis (the 'lytico' part of its name derives from the word 'paralytico'), but it also resembled, in some cases, a form of Parkinson's disease or dementia. The difference was, it occurred in people between the ages of twenty-five and forty. Obviously, it was terrifying, but it was rare, until World War II. In the 1940s, the rate of the disease started climbing. In 1946, cases spiked so high that it became one of the leading causes of death of the Chamorro population. This continued into the middle of the 1960s, and then rates declined again.

Lytico Bodig has multiple different courses. Some patients begin to slow down. They have trouble moving and fall over backwards. Some patients become forgetful, as if they have a version of Alzheimer's. Still another form of the disease causes people to slowly lose feeling in their limbs. As the disease progresses, their body loses the ability to move, while their mind stays clear. Some accounts of this form of the disease say that the patients lose the ability to speak on their own, but can reply freely to anything said to them.

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Because of the effects of the war on the various countries it touched, it's natural to think that the disease had something to do with the effects of World War II. And yet modern day scientists, when studying Lytico-Bodig in people who move to Guam, note that it takes about ten years of residence on the island before anyone falls ill. Since the disease tended to run in families, scientists began investigating a genetic link, but found nothing. The search moved to lifestyle, which families also tend to share. Some scientists think that flour made from cycads, a plant with psychoactive compounds in its seeds and toxins in its starchy roots must have caused the disease. Others say that the roots and flour were washed so thoroughly that the toxin couldn't remain in great enough concentration to cause the disease. Some researchers blame cyanobacteria in the sea, which are eaten by sea creatures and make their way into the diet of local people.

A very popular theory held that bats were the cause. The bats ate the cycad fruit, and the toxins were concentrated in their flesh. When people ate the flesh of the bats, they were exposed. Lending credence to this theory was the fact that, when the disease declined in the 1960s, the bats had been hunted to extinction on Guam. The same species of bats on neighboring islands were imported and eaten, but those bats had a different diet, which didn't include the fruit of the cycads.

No theory really answers the question of why the rate of the disease spiked when it did, or why it lingers on. Scientists still study the disease, hoping to discover its cause, as well as gain insight into similar neuro-degenerative diseases. But, as cases dwindle, it looks like the questions about this recent mystery plague will remain.